Robots with legs should be able to go where wheeled robots cannot – over obstacles and crevices.

The problem has been that legged robot have been ungainly and have needed a lot of energy to get around.

A team of researchers at MIT may have figured out a way to make a four-legged, cheetah-like robot run and jump more gracefully and efficiently. To get there, they studied animals like dogs and cats and used that biological information to create a new algorithm for bounding.
"Our robot is about 20 times more efficient than other quadruped robots," Sangbae Kim, an associate professor of mechanical engineering at MIT, told Computerworld. "Our robot is as efficient as a real animal … and it can run much longer because it's efficient."

The robot, which is about 3 feet tall and 3 feet long, can sprint up to 10 mph. It also can jump a foot high and make a leap more than a foot long. Kim said the Cheetah robot has used only about 40% of its power, and is expected to eventually jump much higher and reach a running speed of about 30 mph. The researchers are slowing increasing the robot's power so they don't risk damaging it.
The cheetah, which uses an electric motor, does not have a communications or power tether.
Kim said the key to the bounding algorithm lies in programming each of the robot's legs to exert a specific amount of force in that moment when the feet hit the ground.

"We studied a lot of biology," he said "I studied a lot of mechanics of quadrupeds, like cats and dogs. We studied how the brain controls the legs. There were a lot of small bits of information that we got from animals -- the way they bound, trotted and galloped, and the way those motions changed over a wide range of speeds. We directly utilized that to be able to control the force of the legs better. To know how much force I need to exert each step, I need to know so much about the mechanics."

Once the engineers calculated how long a leg – whether biological or robotic – needs to be on the ground and how long in the air, they were able to figure out how much force to apply to that leg to compensate for the gravitational force. That information enabled them to control the machines bounding at different speeds.

To enable the robot to jump, they simply tripled the force.

Boston Dynamics, a robotics company acquired by Google, has gained attention with its BigDog robot, a four-legged machine designed to travel across rough terrain. However, the BigDog has a fairly awkward and ungainly gait.

Kim noted that MIT's Cheetah has a smoother gait, is quieter and uses less energy than BigDog.

"Most robots are sluggish and heavy, and thus they cannot control force in high-speed situations," Kim said. "That's what makes the MIT Cheetah so special. You can actually control the force profile for a very short period of time, followed by a hefty impact with the ground, which makes it more stable, agile,and dynamic."

He added that a key robotics advance is the Cheetah's ability to balance itself while running and jumping.

Imagine being in a field and finding a rock, Kim said. "In this case, [the robot] can jump over it. The whole point of having legs is sending [the Cheetah] where a wheeled robot cannot go. A lot of cars go nicely on the road, but there are many things wheels cannot go over. With this we are realizing the actual function of the legs."

Source: computerworld.com